Method of seasoning crystalline ceramic discharge lamps

ABSTRACT

A method of seasoning arc tubes for ceramic discharge lamps in which the arc tubes are operated at the rated wattage for the lamp for about 3 to 5 minutes and the power input is thereafter increased to from 2 to 3 times the rated wattage of the lamp and the arc tubes are operated at this high wattage for a period of from 2 to 3 minutes to thereby stabilize the voltage, and increase the lumen output and lumen maintenance.

Unlted States Patent [151 3,682,525 Knochel et a1. [45] Aug. 8, 1972 METHOD OF SEASONING 3,342,538 9/1967 Mitrofanor ..3l6/22 CRYSTALLINE CERAMIC DISCHARGE 3,474,277 10/1969 Zollweg et al. ..3l3/220 LAMPS 3,497,756 2/1970 Knochel et al ..3l3/220 X 3 551 719 12/1970 Peacher et a1. ..313/220 X [72] Inventors: William J. Knochel West Orange;

Leo Werner, Cear Grove, both 2,290,208 7/1942 Quame ..3l6/l X of Primary ExaminerJohn F. Campbell Asslgnee! wesmghom Electric Corporation, Assistant ExaminerRichard Bernard Lazarus Plttsburgh, Attorney--A. T. Stratton, w. D. Palmer and Blair sm- 22 Filed: June 26,1970 debake' [21] Appl. No.: 50,180 57 ABSTRACT A method of seasoning arc tubes for ceramic 5" 29/25- discharge lamps in which the arc tubes are operated at e. th f f 3 t 5 [58] Fleld of Search ...29/25.1, 25.11, 25.16; 316/22, minutes and the power input is thereafter increased to 316/26 1 from 2 to 3 times the rated wattage of the lamp and the arc tubes are operated at this high wattage for a [56] References Cited period of from 2 to 3 minutes to thereby stabilize the UNIT PATENTS voltage, and increase the lumen output and lumen t 682,699 9/1901 Hewitt ..316/22 mm enance 1,922,245 8/1933 Hunter, Jr. ..3l6/22 5 Claims, 2 Drawing Figures PATENTEIIAUB 8 912 3.682.525

OPERATE ARC TUBE AT RATED WATTAGE FOR FROM 3T0 5 MINUTES INCREASE OPERATING WATTAGE TO FROM 2 TO 3 TIMES RATED WATTAGE OPERATE ARC TUBE AT FROM 2 T0 3 TIMES RATED WATTAGE FOR FROM 2 TO 3 MINUTES PERMIT ARC TUBE TO COOL TO ROOM TEMPERATURE FIG. 2

WITNESSES I INVENTORS fi-ml'ww William J. Knochel & f 7' 9 Leo C. Werner ATTORNEY BACKGROUND OF THE INVENTION This invention relates to ceramic discharge lamps and more particularly to a method of seasoning the arc tube for a ceramic discharge lamp which improves the lamps rated lumen output and lumen maintenance during the life of the lamp.

Seasoning of the arc tube is a common practice in the manufacture of gas discharge lamps and particularly gas discharge lamps employing ceramic arc tubes. The arc tubes are seasoned (i.e., operated for a period of time) to set the emission material in the electrode as well as to stabilize the lamp voltage. Seasoning further serves as an operational test of the lamp.

Conventional seasoning practices require that the arc tubes be operated for two hours on an inductive type ballast capable of supplying approximately 400 watts of power at about 100 volts and 4 amps. The lamps are thereafter tested on a high voltage pulse type ballast and were in the past accepted if they performed between the voltage limits of 70 and 115 volts and had a minimum light output or efficiency of a 105 lumens per watt. Lamps rejected for low output were usually those having a grey to a darker grey coloring of the ceramic body which is believed to be caused by sodium contamination of the arc tube body. It will be apparent that the long seasoning time, i.e., 2 hours for a conventional seasoning process, provides a significant problem with respect to the efficient production of ceramic discharge lamps.

SUMMARY OF THE INVENTION The seasoning method of this invention while significantly reducing the seasoning time required in the manufacture of ceramic discharge lamps has also, unexpectedly, improved the voltage stabilization of the lamp, increased the efficiency of the lamp by clearing up contaminated arc tubes and has provided for improved lamp maintenance during the life of the lamp.

The seasoning method of this invention accomplishes the foregoing improved results through the steps of operating the arc tube at its rated wattage for a first predetermined time, thereafter increasing the operating wattage to a second wattage level of about 2 to 3 times the rated wattage of the lamp, maintaining the second wattage level for a second predetermined time and thereafter removing the arc tube from its source of electrical energy.

BRIEF DESCRIPTION OF THE DRAWINGS The above described method along with its attendant advantages will become more readily apparent and better understood as the following detailed description is considered in connection with the accompanying drawings in which:

FIG. 1 is a sectional view of a typical ceramic arc tube; and

FIG. 2 is a block diagram illustrating the steps employed in practicing the method of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A typical arc tube for a ceramic discharge lamp is illustrated in FIG. 1 and is generally designated 10. The arc tube includes a ceramic body 12 generally of polycrystalline alumina which is closed off at each end by a refractory metal end cap 14 usually constructed from niobium. The are tube is conventionally mounted within the lamp at one end by a lead-in conductor 16 of tantalum or niobium which is brazed by means of a suitable brazing composition 17 to the end cap 14. At the other end refractory metal exhaust and fill tubulation 18 extends through the end cap 14 and is generally constructed from tantalum and brazed as at 19 to the end cap 14. The exhaust and fill tubulation 18 serves to permit the interior of the arc tube to be exhausted and filled with an inert ionizable starting gas as well as the discharge sustaining constituents. Arc supporting electrodes 20 are mounted within the arc tube at each end thereof and are generally of tungsten with an emission material such as thorium impregnated between the coils. The electrodes 20 are mounted within the arc tube on refractory metal support straps 22 and 24 which serve to both mount the electrodes 20 within the arc tube and electrically connect the electrodes to the lead-in conductors 16 and 18, respectively.

A typical arc tube for a ceramic discharge lamp of the most common, 400 watt, type will be constructed of tubular polycrystalline alumina or sapphire having a three-eighths inch outside diameter, a 0.30 inch wall thickness and approximately a 4% inch length. The conventional arc tube for a 400 watt ceramic discharge lamp includes as a part of the filling from between about 15 to 18 millimeters of an inert ionizable starting gas, as for example xenon, and a discharge sustaining fill 26 which may be for example, about 20 milligrams of mercury and about 8 /2 milligrams of sodium. After the arc tube is exhausted, filled with the inert ionizable starting gas and the discharge sustaining filling, the tantalum tubulation 18 is then sealed off by means by a pinched seal as illustrated in phantom at 28.

At this point in the manufacture of the lamp conventional manufacturing processes dictate that the arc tube be seasoned for about 2 hoursat 400 watts for the purpose of setting the emission material in the electrode and stabilizing the lamp voltage as well as to test the lamp for various operating characteristics to assure that the lamp would meet minimum standards for an acceptable lamp. Many lamps under this testing procedure would have to be rejected for reasons of not meeting minimum voltage requirements or not meeting minimum requirements as to efficiency (i.e., lumens per watt) of light output. One reason for the low light output of lamps seasoned in this fashion is attributed to a grey-to-dark-grey coloring displayed after seasoning by some of the ceramic arc tubes which were, prior to seasoning, a translucent, almost pure white, body color.

The seasoning method of this invention, while significantly reducing the time required to season an arc tube for a ceramic discharge lamp, additionally provides many unexpected improvements in the final product. In accordance with the present invention, are tubes are seasoned at their designed operating wattage for a first predetermined time and the power is thereafter increased to a second operating wattage which is about 2 to 3 times the rated wattage for the are tube and this second wattage level is maintained for a second predetermined time. For example, a 400 watt arc tube is seasoned in accordance with the present invention at its rated wattage, 400 watts, for about minutes. The power is then increased to about 1,000 watts and the arc tube maintained at the 1,000 watt level for about 3 minutes. Another common wattage for a ceramic discharge lamp is the 250-275 watt size which in accordance with this invention is seasoned for about 3 minutes at the 250-275 watt level and thereafter the power is increased to 800 watts and the arc tube operated at that power level for about 2 to 3 minutes. Higher wattage lamps i.e., 1,000 watt rating are high wattage seasoned at proportionately higher wattages.

Under the old 2 hour seasoning method efficiencies of between 100 to 105 lumens per watt were considered acceptable whereas the average lamp seasoned by the process of this invention has a minimum efficiency of about 1 l5 lumens per watt. In addition, the minimum voltage level of an acceptable lamp of the 400 watt size is considered to be between about 90 and 115 volts whereas voltage limits between 70 and 115 volts were acceptable under the old seasoning method. No longer are arc tubes rejected for low light output because of grey-to-dark-grey colored ceramic arc tubes. Arc tubes that were seasoned under the old method and presented grey-to-dark-grey colored ceramic bodies, which limited light output, were cleaned up and returned to their near white appearance by additional seasoning in accordance with the instant method. It is believed that the grey-to-dark-grey color was caused by sodium contamination of the polycrystalline alumina body member and that the much higher temperatures associated with the 1,000 watt operation causes a clean up of sodium from the arc tube body. In addition, foreign gases are driven into the hot metallic parts of the electrode mounting support and end cap which cleans up the enclosed atmosphere. An additional advantage of the high wattage seasoning is the shock test which it provides for the ceramic bodied arc tubes. Arc tubes subjected to the high wattage seasoning of this invention which do not fail from thermal shock during seasoning will never fail from thermal shock during operation as a lamp.

Another unexpected result attributed to the high wattage seasoning of this invention is the increased lumen maintenance during the life of the lamp. Lamps seasoned in accordance with this invention have been operated from between 8,000 and 9,000 hours with a less than a 5 percent drop in lumen output after 9,000 hours. For example, lamps operating initially at 400 watts between and 118 lumens per watt after 10,000 to 15,000 hours still exhibited an efficiency of from between 1 l0 and l 14 lumens per watt.

As will be apparent from the foregoing, the high wattage seasoning method of this invention has contributed significantly to the production of an improved ceramic discharge lamp exhibiting better voltage stabilization, higher lumen output, better lumen maintenance and a higher percentage of acceptable lamps in addition to substantially reducing the time required for arc tube seasoning.

lY1 l$TfiethQd of seasoning a finally sealed and completed arc tube for a crystalline ceramic discharge lamp comprising the steps of:

operating said finally sealed and completed arc tube at its rated wattage for a first predetermined time of at least about 3 minutes;

increasing said operating wattage to a second wattage level of about 2 to 3 times the rated wattage of said are tube; and

maintaining said second wattage level for a second predetermined time.

2. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said first predetermined time is from about 3 to 5 minutes.

3. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said second predetermined time is from about 2 to 3 minutes.

4. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said first predetermined time is from about 3 to 5 minutes and said second predetermined time is from about 2 to 3 minutes.

5. The method of seasoning a finally sealed and completed arc tube for a 400 watt crystalline ceramic discharge lamp which comprises the steps of:

operating said finally sealed and completed arc tube at about 400 watts for from about 3 to 5 minutes; thereafter increasing the operating wattage of said are tube to from between about 800 and 1,200 watts; maintaining said 800 to 1,200 watt level for from about 2 to 3 minutes, and thereafter permitting said are tube to cool to room temperature. 

1. The method of seasoning a finally sealed and completed arc tube for a crystalline ceramic discharge lamp comprising the steps of: operating said finally sealed and completed arc tube at its rated wattage for a first predetermined time of at least about 3 minutes; increasing said operating wattage to a second wattage level of about 2 to 3 times the rated wattage of said arc tube; and maintaining said second wattage level for a second predetermined time.
 2. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said first predetermined time is from about 3 to 5 minutes.
 3. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said second predetermined time is from about 2 to 3 minutes.
 4. The method of seasoning an arc tube for a ceramic discharge lamp according to claim 1 wherein said first predetermined time is from about 3 to 5 minuTes and said second predetermined time is from about 2 to 3 minutes.
 5. The method of seasoning a finally sealed and completed arc tube for a 400 watt crystalline ceramic discharge lamp which comprises the steps of: operating said finally sealed and completed arc tube at about 400 watts for from about 3 to 5 minutes; thereafter increasing the operating wattage of said arc tube to from between about 800 and 1,200 watts; maintaining said 800 to 1,200 watt level for from about 2 to 3 minutes, and thereafter permitting said arc tube to cool to room temperature. 